A number of different ignition systems for igniting fuel in internal combustion systems has been proposed. These ignition systems generally fall into three main types: conventional arc discharge, classic plasma discharge, and corona discharge.
In a conventional arc or inductive ignition system, an ignition coil is charged on a primary winding with a DC voltage, and a finite quantity of energy is stored in the ignition coil. At some predefined ignition point, the current flow to the primary winding of the ignition coil is turned off, and a portion of the energy stored in the ignition coil is discharged from a secondary winding of the ignition coil across a spark gap of a spark plug to ground. In this discharge, the voltage at the spark plug gap increases until the potential is large enough to create an arc across the spark plug electrodes to ground. The stored energy from the ignition coil is quickly discharged through the arc to ground in a single discharge event, until the energy is dissipated to the point to which it can no longer sustain the arc. In this type of ignition system, the current in the arc during the discharge event is limited to a moderate level by the relatively high resistance in the secondary circuit, and the arc voltage is relatively low. The arc itself is highly ionized and has relatively low resistance to ground.
In a classic plasma ignition system there is generally an additional capacitive energy storage that is used to significantly increase the energy stored before discharge across a spark gap. In this system, a capacitor is typically not high enough voltage to initiate an arc across the spark gap, so a conventional inductive ignition coil system is used to initiate the discharge path. Once a discharge path is established, the energy stored in the capacitor can be discharged extremely rapidly in a high current burst of energy and at a relatively low voltage. This fast, high energy discharge creates a visible plasma in a single discharge. Once the energy is dissipated from both the ignition coil and from the capacitor, an arc and plasma go out and the event is over.
U.S. Patent Pub. No. 2008/0141967 (Tani) is an example of a classic plasma ignition system. This patent publication discloses a plasma ignition device that includes a plasma ignition plug having an alumina insulation member to insulate a center electrode from a ground electrode, and electric power supply circuits to apply high voltages to the plasma ignition plug. The plasma ignition device activates the gas in a discharge space of the insulation member into the plasma of a high temperature and a high pressure by the high voltage applied between the center electrode and the ground electrode and injects the same into an internal combustion engine. The electric power supply circuits are connected to the center electrode as an anode and to the ground electrode as a cathode.
A corona discharge system typically does not include a stored energy device. As a result, energy is not discharged in a single event. A conventional spark ignition produces a fixed duration ignition event. A corona ignition device can produce an ignition event for a controlled period of time.
U.S. Pat. No. 6,883,507 (Freen) discloses an example of a corona discharge system. The system comprises an electrode inside of a combustion chamber, an electric circuit which provides radio frequency electric power to the electrode, and a ground formed by the combustion chamber walls. A radio frequency voltage differential formed between the electrode and the ground produces a radio frequency electric field therebetween, which creates a non-thermal plasma, resulting in combustion of the fuel-air mixture. A boron nitride insulator surrounds the electrode. The system can be utilized in engines such as internal combustion engines or gas turbine engines.
More efficient igniter systems for igniting fuel in internal combustion engines are needed. In particular, igniter systems that provide highly effective dielectric and mechanical properties under the extreme temperature, mechanical stress and pressure conditions of the combustion environment are desired.